Most smokers and smokeless tobacco (ST) users begin before the age of 18. In adolescents, the prevalence of ST use has been increasing and the prevalence of dual use for ST use and smoking is high, and even higher in Ohio than many other states. The current marketing environment will likely make this increase. However, almost nothing is known about adolescent initiation of ST and dual use with their trajectories to regular use and dependence;exposures through biomarkers, and;environmental and genetic risk factors. This project ad- dresses 3 FDA research priorities: 1)